1. Field of the Invention
This invention relates generally to apparatus and methods for producing heat exchange with body tissue, and more specifically to methods and apparatus for the hypothermic treatment of a body fluid in a body conduit.
2. Discussion of the Prior Art
Many of the advantages of hypothermia are well known. By way of example, it has been found particularly desirable to lower the temperature of body tissue in order to reduce the metabolism of the body. In stroke and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. Hypothermia inhibits brain edema and lowers intracranial pressure.
In the past, hypothermic treatment has been addressed systemically, meaning that the overall temperature of the entire body has been lowered to achieve the advantages noted above. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. An example of this systemic approach includes catheters for transferring heat to or from blood flowing within a patient's vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. A closed loop heat exchange catheter is also disclosed by Saab in U.S. Pat. No. 5,624,392. Some of the disadvantages of systemic hypothermia include cardiac arrhythmia, pulmonary edema and coagulopathies. Systemic hypothermia also results in hypotension and various immunodeficiencies.
The systemic approach is not always advantageous when the beneficial effects are desired locally at the focus of the operative procedure and only the disadvantages of hypothermia are felt throughout the remainder of the body.
More recent focus has been directed to producing hypothermia in localized areas of the body, leaving the remainder of the body to function at a normal body temperature. These localized applications of hypothermia have been external, relying for example on cooling helmets or cooling neck collars to produce localized hypothermia for the brain.